Displaying a Query - True/False or Neither

A really dumb question, I’m afraid - I’m sure I am missing something very simple.

I am designing a query on my names & addresses database which includes several ‘true/false’ fields. When I look at the result on screen to confirm it is doing what I want, the T/F fields are displayed as small squares. However, they have 3 styles instead of the two I would expect. Some contain a tick where I would expect to see one, some are empty where I would expect them to be empty; but some contain a solid black centre! These black ones seem to correspond to ‘false’ entries, but so do the empty ones. If I click on a black square I can cycle through a tick and a blank and back to black again. I have confirmed by trial and error that doing this does change the underlying data (ie if I turn a black square to a tick, the corresponding record is edited to show ‘true’ in that field)

What do the black squares mean, and how can I stop them appearing?

The solid squares (depends upon system - could be dash or dimmed check mark) is the tri-state value of NULL. See this post and this post.

Thanks for that explanation, Ratslinger. I hadn’t realised that there was a separate (third) state of NULL. Now all I have to do is work out how to change the field properties to ‘mandatory’ without building the database again from scratch . . .

The basic explanation is that my original assumption was wrong - there are not just 2 states for a Boolean field of TRUE or FALSE, a third state of NULL is possible unless the field is made mandatory.

This does not answer my other problem of how to stop it happening after the fields have already been defined.

In the checkbox control properties (General tab), set Tristate value to No.